1. Field of the Invention
The present invention relates to a magnetic head suspension for supporting a magnetic head slider that reads and/or writes data from and to a recording medium such as a hard disk drive.
2. Related Art
Due to the increase in capacity of a magnetic disk device, a magnetic head suspension is required to prevent, as much as possible, displacement of a magnetic head slider from a target track even in a case where the magnetic head suspension is swung about a swing center at a higher speed so that the magnetic head slider is quickly shifted onto the target track.
For example, Japanese Unexamined Patent Publication No. 2005-032393 (hereinafter, referred to as Prior Art Document 1) discloses a magnetic head suspension including a load beam part that has a main body portion in a flat plate shape and paired right and left ribs (flange portions) extending respectively from side edges of the main body portion so as to be apart from a disk surface. In this magnetic head suspension, the respective side edges of the main body portion are inclined toward a suspension longitudinal center line such that the load beam part is gradually reduced in width as it advances from a proximal end to a distal end in the suspension longitudinal direction. Further, each of the ribs is at least partially curved to form a narrowed portion in a planar view along a direction perpendicular to the disk surface.
The magnetic head suspension disclosed in Prior Art Document 1 is regarded such that the provision of the narrowed portions reduces the weight of the load beam part, thereby allowing the resonant frequency of the load beam part to be higher than the conventional configurations.
As described above, Prior Art Document 1 discloses the feature that the resonant frequency can be raised by the narrowed portions provided to the flange portions of the load beam part. However, it is unknown in Prior Art Document 1 which one of various vibration modes is focused on with regard to the resonant frequency possibly generated to a magnetic head suspension.
Japanese Unexamined Patent Publication No. 2008-021374 (hereinafter, referred to as Prior Art Document 2) discloses a magnetic head suspension including an elastic deformation portion and a main body portion that extends forward from the elastic deformation portion. The main body portion includes a first member and a second member. The first member is gradually reduced in width as it advances to a front end and is provided with flanges at right and left side edges thereof. The second member is substantially in a T-letter shape, and has a wide portion provided at a proximal edge with a flange and a narrow portion extending forward from the wide portion. The narrow portion has a width smaller than that of the main body portion, and is provided at right and left side edges with flanges.
In Prior Art Document 2, the first and second members are joined with each other to form an assembly, which integrally configures a load bending part and a load beam part.
In other words, the elastic deformation portion configures the load bending part, and the main body portion and the second member configure the load beam part.
More specifically, the side edges of the main body portion are provided with the flanges and are inclined so as to be gradually come closer to the suspension longitudinal center line as they advance to the respective front ends. The side edges of the narrow portion are provided with the flanges and extend substantially in parallel with the suspension longitudinal center line at positions closer to the center line than the side edges of the main body portion.
Accordingly, the load beam part configured by the main body portion and the second member has the right and left side edges that are provided with the flanges substantially in the entire areas in the suspension longitudinal direction. The side edges have proximal end regions that are respectively inclined at a first inclination angle with respect to the center line so as to be gradually closer to the center line as they advance to the respective front ends, and distal end regions that extend substantially in parallel with the center line.
In the magnetic head suspension disclosed in Prior Art Document 2, the distal end region of the load beam part is configured by the narrow portion, thereby successfully reducing the width of the load beam part as compared to the conventional cases. This will lead to the reduction of the moment of inertia of the load beam part about a twist center line (or torsion center line) along the center line so as to raise the resonant frequency in a first torsion mode.
The vibrations of the torsion mode that generate in a magnetic head suspension include, in addition to the first torsion mode, a second torsion mode and a third torsion mode.
Nevertheless, Prior Art Document 2 refers only to the vibration in the first torsion mode, and fails to take into consideration the vibration in the second torsion mode and the vibration in the third torsion mode.
More specifically, in a case where the frequency of a drive signal of the actuator is raised in order to shift more quickly the magnetic head slider onto a target track, a resonant vibration in the first torsion mode is generated to the magnetic head suspension when the frequency of the drive signal reaches a certain frequency (hereinafter, referred to as a first resonant frequency).
In a case where the frequency of the drive signal is further raised beyond the first resonant frequency, upon reaching another certain frequency (hereinafter, referred to as a second resonant frequency), a resonant vibration in the second torsion mode is generated to the magnetic head suspension. In a case where the frequency of the drive signal is furthermore raised beyond the second resonant frequency, upon reaching still another certain frequency (hereinafter, referred to as a third resonant frequency), a resonant vibration in the third torsion mode is generated to the magnetic head suspension.
In the resonant vibration in the first torsion mode, in a state where a position at which the load bending part and a position at which the dimple of the load beam part are arranged so as not to be displaced in a z direction perpendicular to the disk surface (namely, the positions form nodes), only the load beam part is principally twisted about the twist center line along the suspension longitudinal center line so that a substantially center portion between the two nodes in the suspension longitudinal direction is displaced to the maximum in the z direction (namely, the substantially center portion forms an antinode).
In the resonant vibration in the second torsion mode, in a state where three positions form the nodes, the three positions including a position at which the supporting part is rigidly fixed with respect to the z direction (in a case where the supporting part is configured by a base plate, a position of a boss portion that is fixed by caulking to a carriage arm coupled to an actuator; hereinafter, referred to as a supporting part fixed position), a position at which the dimple is arranged, and a halfway position of the load beam part that is located at a substantially center in the suspension longitudinal direction between the supporting part fixed position and the position of the dimple, the distal end region of the supporting part, the load bending part and the load beam part are twisted about the twist center line along the suspension longitudinal center line so that two portions form the antinode, the two portions including a substantially center portion between the supporting part fixed position and the halfway position of the load beam part in the suspension longitudinal direction and a substantially center portion between the halfway position of the load beam part and the position of the dimple in the suspension longitudinal direction.
In the resonant vibration in the third torsion mode, in a state where four positions form the nodes, the four positions including the supporting part fixed position, the position of the load bending part, the position of the dimple and the halfway position of the load beam part that is located at a substantially center in the suspension longitudinal direction between the position of the load bending part and the position of the dimple, a first portion located between the supporting part fixed position and the position of the load bending part is twisted in a first direction about the twist center line along the suspension longitudinal center line, a second portion located between the position of the load bending part and the halfway position of the load beam part is twisted about the twist center line in a second direction, which is reverse to the first direction, and a third portion located between the halfway position of the load beam part and the position of the dimple is twisted about the twist center line in the first direction.
Therefore, in order to maintain the favorable positioning accuracy of the magnetic head slider onto the target track, as well as in order to increase the swing speed of the magnetic head suspension about the swing center by the actuator thereby to reduce as much as possible the time required to shift the magnetic head slider onto the target track, not only the resonant frequency in the first torsion mode but also the resonant frequencies in the second and third torsion modes need to be raised as high as possible, so that the resonant vibration in any one of the first to third torsion modes is less likely to occur in the magnetic head suspension.